How did the row start?

The row initially began shortly after Gordon Brown shocked the political world by reappointing Peter Mandelson, then the EU's trade commissioner and a sworn enemy of the prime minister, to the cabinet.

Soon afterwards it was claimed that Mandelson had "dripped pure poison" about him during a meeting with George Osborne two months earlier at Taverna Agni on the Greek island of Corfu.

Both men admitted the meeting took place, but, angry at the allegations, Mandelson threatened to reveal what the shadow chancellor had told him privately about the Conservatives.

The debacle raised questions about the prime minister's decision to bring Mandelson back into the cabinet after he was twice forced to resign from the government under Tony Blair's leadership.

What has that got to do with a Russian oligarch and his yacht?

One week later, the Sunday Times claimed Mandelson gave trade concessions worth up to £50m a year to Russia's richest man after being entertained by him on his "superyacht".

The encounter on the 238ft (73m) Queen K in Corfu this summer was said to be the latest in a series of social meetings between Mandelson and Oleg Deripaska - known as the "king of aluminium" - during Mandelson's term as trade commissioner.

The paper claimed that in the past three years Mandelson had twice acted to cut European aluminium import duties and Deripaska's company Rusal, the world's largest producer of aluminium, was one of the main beneficiaries.

At the time of Mandelson's Corfu holiday his trade department was a few weeks into a fresh investigation into aluminium foil tariffs that could have hit one of Deripaska's companies, the Sunday Times said.

A spokesman for Mandelson said: "They had been on holiday in the same area and it was purely a social occasion."

It subsequently emerged that Mandelson actually stayed on the yacht as a guest of Nathaniel Rothschild, the hedge fund manager and son of Lord and Lady Rothschild. Rothschild, the Times reported, had run out of room at his house.

The Liberal Democrats warned that Mandelson "needs to be extremely careful about any potential conflicts of interests" and said he should "not have been accepting hospitality from a billionaire who is a clear beneficiary of his policy decisions as European commissioner".

Why have the Tories now been dragged into the row?

Annoyed at reports of "what may or may not have happened at a private gathering" of his friends, Rothschild has written a letter in today's Times, claiming George Osborne, the Tory shadow chancellor, also accepted his hospitality and "found the opportunity of meeting with Mr Deripaska so good that he invited the Conservatives' fundraiser Andrew Feldman, who was staying nearby, to accompany him to Mr Deripaska's boat to solicit a donation."

Rothchild also claimed that Feldman suggested in a subsequent conversation, at which Deripaska was not present, that as Deripaska is not British and accepting a donation from him would breach party funding rules, that the donation could be "channelled" through one of Deripaska's British companies.

How does Osborne know Rothschild?

The two went to the University of Oxford together and were both members of the Bullingdon Club. Rothschild's mother helped fund Osborne's office. Osborne was reportedly staying with Rothschild on the Greek island of Corfu.

But in his letter to the Times, Rothschild warns the paper its "obsession with Mr Mandelson is trivial in light of Mr Osborne's actions".

What do the Tories say about the debacle?

The Conservatives deny "absolutely" that Osborne or Feldman attempted to solicit a donation from Deripaska.

"Nor did they suggest a method by which he could conceal a donation via a British company," the party said in a statement.

"Donations to the Conservative party were not discussed with Mr Deripaska. Rothschild suggested to Andrew Feldman that Mr Deripaska wanted to make a donation to the party through one of his British companies. The offer was not taken up."